Isocyanates, highly reactive compounds used extensively in industry, are the most commonly reported cause of occupational asthma. However, the mechanisms by which isocyanates cause asthma are not well defined. Limited information suggests that isocyanates can act like a foreign low molecular weight hapten, causing antigen specific T cell responses and airway inflammation. We performed isocyanate challenge studies to characterize the lung responses, and have documented late and/or asthmatic responses. Airway biopsies showed increased inflammatory cells, primarily T cells. BAL and peripheral blood showed increased activated and/or memory T cells with isocyanate challenge. This information has lead us to formulate the following hypothesis: a) Isocyanate asthma is mediated by a distinctive airway inflammatory response characterized by prominent T cell abnormalities, b) Isocyanates induce an antigen specific T cell response in susceptible individuals, and c) Knowledge of the role of T cells in the pathogenesis of isocyanate asthma may lead to identification of peripheral blood mar(s) of sensitization, early isocyanate asthma, and/or host susceptibility. To address these hypothesis we propose to : Aim 1) Characterize inflammatory responses in the airway biopsies, BAL, and peripheral blood of subjects with isocyanate asthma and appropriate controls before and after specific isocyanate challenge. Immunohistochemistry, FACS analysis, RT-PCR, in situ hybridization, and ELISA approaches will be used to characterize the: a) phenotypes, activation status, and anatomic location of T lymphocytes, b) expression of t cell activating and regulating cytokines, c) T cell receptor (TCR) Vbeta gene usage, and d) expression and distribution of endothelial adhesion molecules. Aim 2) Characterize hapten-specific T cell responses induced by isocyanates in vitro. We will: a) Determine proliferation responses and levels of cytokine production of BAL and peripheral blood mononuclear cells following stimulation with specific isocyanate conjugates and/or isocyanate-conjugated antigen presenting cells and b) Generate and characterize isocyanate-specific T cell clines cultured from airway biopsies. Aim 3) Identify peripheral blood markers of early disease and/or susceptibility to isocyanates that eventually can be applied to larger epidemiologic studies. These studies should improve our understanding the pathogenesis of isocyanate asthma, in particular the role of T cells, and may be applicable to other forms of asthma. These studies should also identify markers of sensitization, early disease and/or host susceptibility to isocyanates that will enable early diagnosis and prevention.